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Abstract:

The invention relates to a tire comprising at least one rubber
composition based on at least one diene elastomer, one reinforcing
filler, one chemical crosslinking agent and one modifying agent, chosen
from the compounds of following formula (I):
##STR00001## where R denotes a unit comprising at least one reactive
group, R1 denotes hydrogen, R2 denotes an alkylene radical
comprising from 2 to 8 carbon atoms and optionally one or more
heteroatoms chosen from S, N, O or Si, A denotes an oxygen or sulphur
atom or an ═NH group, preferably an oxygen atom.

Claims:

1. Tire comprising at least one rubber composition based on at least one
diene elastomer, one reinforcing filler, one chemical crosslinking agent
and one modifying agent, optionally pregrafted to the diene elastomer,
chosen from the compounds of following formula (I): ##STR00008##
wherein R denotes a unit comprising at least one reactive group, R1
denotes hydrogen, R2 denotes an alkylene radical comprising from 2
to 8 carbon atoms and which may optionally be substituted or interrupted
one or more heteroatoms chosen from S, N, O or Si, A denotes an oxygen or
sulphur atom or an ═NH group.

2. Tire according to claim 1, wherein R denotes an --R3X unit, where
R3 denotes a C2-C50 alkylene radical which can be
substituted or interrupted by one or more nitrogen, oxygen, sulphur and
silicon atoms and X is a reactive group.

3. Tire according to claim 1, wherein the diene elastomer is chosen from
natural rubber, synthetic polyisoprenes, polybutadienes, butadiene
copolymers, isoprene copolymers and the mixtures of these elastomers.

4. Tire according to claim 1, wherein the reinforcing filler is composed
of an organic reinforcing filler, an inorganic reinforcing filler or a
blend of organic reinforcing filler and inorganic reinforcing filler, and
wherein the content of reinforcing filler in the composition is between
30 and 150 phr.

7. Tire according to claim 4, wherein the reinforcing filler comprises a
blend of silica and carbon black.

8. Tire according to claim 1, wherein the chemical crosslinking agent is
composed of from 0.5 to 12 phr of sulphur, or of from 0.01 to 10 phr of
one or more peroxide compounds.

9. Tire according to claim 1, wherein the content of modifying agent
varies from 0.05 to 10 mol %.

10. Tire according to claim 9, wherein the content of modifying agent
varies from 0.1 to 2 mol %.

11. Tire according to claim 1, wherein the reactive group or groups of
the R unit are chosen from amine, thiol, epoxy, isocyanate, anhydride,
alcohol and carboxylic acid groups, preferably amine and thiol groups.

13. Tire according to claim 1, wherein the rubber composition further
comprises one or more diene elastomers grafted or ungrafted by a
modifying agent of formula (I).

14. Process for preparing a tire rubber composition based on at least one
diene elastomer, one reinforcing filler and one chemical crosslinking
agent, comprising: grafting, to the diene elastomer, a modifying agent
chosen from the compounds of following formula (I): ##STR00009## where
R denotes a unit comprising a reactive group, R1 denotes hydrogen,
R2 denotes an alkylene radical comprising from 2 to 8 carbon atoms
and optionally substituted or interrupted by one or more heteroatoms
chosen from S, N, O or Si, A denotes an oxygen or sulphur atom or an
═NH group, incorporating, in the diene elastomer thus grafted by the
modifying agent, the reinforcing filler, everything being
thermomechanically kneaded, in one or more goes, until a maximum
temperature of between 130.degree. C. and 200.degree. C. is reached,
cooling the combined mixture to a temperature of less than 100.degree.
C., subsequently incorporating the chemical crosslinking agent, kneading
everything up to a maximum temperature of less than 120.degree. C.,
extruding or calendaring the rubber composition thus obtained.

15. Process according to claim 14, wherein R denotes an --R3X unit,
where R3 denotes a C2-C50 alkylene radical which can
comprise one or more nitrogen, oxygen, sulphur and silicon atoms and X is
a reactive group.

16. Process for preparing a tyre rubber composition based on at least one
diene elastomer, one reinforcing filler and one chemical crosslinking
agent, characterized in that it comprises the following stages:
incorporating, in the diene elastomer, the reinforcing filler and a
modifying agent chosen from the compounds of following formula (I):
##STR00010## where R denotes a unit comprising at least one reactive
group, R1 denotes hydrogen, R2 denotes an alkylene radical
comprising from 2 to 8 carbon atoms and optionally one or more
heteroatoms chosen from S, N, O or Si, A denotes an oxygen or sulphur
atom or an ═NH group, preferably an oxygen atom, everything being
kneaded thermomechanically, in one or more goes, until a maximum
temperature of between 130.degree. C. and 200.degree. C. is reached,
cooling the combined mixture to a temperature of less than 100.degree.
C., subsequently incorporating the chemical crosslinking agent, kneading
everything up to a maximum temperature of less than 120.degree. C.,
extruding or calendaring the rubber composition thus obtained.

17. Process according to claim 16, characterized in that R denotes an
--R3X unit, where R3 denotes a C2-C50 alkylene
radical which can be substituted or interrupted by one or more nitrogen,
oxygen, sulphur and silicon atoms and X is a reactive group.

18. Tire according to claim 1, wherein A is an oxygen atom.

19. Tire according to claim 4, wherein the content of reinforcing filler
is between 50 and 120 phr.

20. Tire according to claim 8, wherein the chemical crosslinking agent is
composed of from 1 to 10 phr.

21. Tire according to claim 10, wherein the content of modifying agent
varies from 0.2 to 1 mol %.

22. Process according to claim 14, wherein A denotes an oxygen atom.

23. Process according to claim 16, wherein A denotes an oxygen atom.

Description:

[0001] The present invention relates to a tire comprising a rubber
composition based on at least one diene elastomer, on a reinforcing
filler, on a chemical crosslinking agent and on at least one specific
modifying agent.

[0002] In the field of the manufacture of tires and in particular on the
formulation of rubber compositions in contact with the ground, known as
treads, the aim is generally to find the best possible compromise between
conflicting performances, such as the rolling resistance and the ability
of the tire to temporarily accept certain strains.

[0003] In particular, it is desirable for the materials forming the treads
to exhibit good stiffness at low and moderate strains, so as in
particular to provide a low rolling resistance, while being capable of
reversibly accepting certain strains and without being damaged under the
effect of greater stresses or strains. In other words, it is desirable to
have available a material which, while being stiff at low and moderate
strains, exhibits a high elongation at break or a high breaking stress.

[0004] It is well known that the chemical crosslinking of elastomers
confers good mechanical and thermal properties thereon. Chemical
crosslinking is characterized by the establishment of covalent chemical
bonds between the polymer chains. Numerous methods for chemical
crosslinking exist. The most widely used methods are those based on
sulphur compounds, of use in the crosslinking of elastomeric materials
comprising unsaturations in their main chains. Another widely used method
is chemical crosslinking with peroxides.

[0005] However, when the number of covalent bonds between the polymer
chains (bridge density) increases, the stiffness at the low and moderate
strains increases but the elongation at break decreases. Conversely, if
the bridge density decreases, the elongation at break increases but the
stiffness at low and moderate strains decreases.

[0006] The Applicant Company has discovered that the compromise between a
good stiffness at low and moderate strain and a high elongation at break
can be obtained by introducing, into the elastomer, a specific density of
the noncovalent bonds between the chains.

[0007] The presence of noncovalent bonds between the chains is generally
known as physical crosslinking or reversible crosslinking. Physical
crosslinking can be obtained by functionalising the chain of the polymer
with chemical molecules capable of associating with one another via
nonpermanent physical interactions, such as ionic interactions, hydrogen
bonds, ion-dipole interactions and dipole-dipole interactions.

[0008] When such an elastomer is formulated in a rubber composition in the
presence of a chemical crosslinking system, covalent bonds appear between
the elastomer chains, which will be additional to the noncovalent bonds.

[0009] In the continuation of the text, "content of modifying agent"
present in a rubber composition is understood to mean, expressed as molar
percentage, the number of molecules of modifying agent present in the
composition per hundred diene elastomer units of the composition, whether
they are, without distinction, diene or nondiene units.

[0010] For example, if the content of modifying agent with regard to an
SBR is 0.20 mol %, this means that there will be 0.20 molecule of
modifying agent per 100 styrene and butadiene units of the SBR.

[0011] In the case where use is made in the composition both of an
elastomer pregrafted with the modifying agent and a diene elastomer not
grafted with a modifying agent, the content of modifying agent represents
the number of molecules of modifying agent grafted per 100 units of diene
elastomers, the number of units taking into account both elastomers
(grafted and ungrafted), it being assumed that other molecules of
modifying agent not pregrafted have not been added to the composition.

[0012] A subject-matter of the invention is thus a tire comprising at
least one rubber composition based on at least one diene elastomer, one
reinforcing filler, one chemical crosslinking agent and one modifying
agent, optionally pregrafted to the diene elastomer, chosen from the
compounds of following formula (I):

##STR00002##

[0013] where

[0014] R denotes a unit comprising at least one reactive group,

[0015] R1 denotes hydrogen,

[0016] R2 denotes an alkylene radical comprising from 2 to 8 carbon
atoms and optionally one or more heteroatoms chosen from S, N, O or Si,

[0017] A denotes an oxygen or sulphur atom or an ═NH group, preferably
an oxygen atom.

[0018] The crosslinking bridges comprising covalent bonds are formed by
virtue of the presence of the chemical crosslinking system. The
crosslinking bridges comprising noncovalent bonds are formed by the
presence of the associative groups of the modifying agent once grafted
along the chain of the elastomer.

[0019] Another subject-matter of the invention is a process for preparing
a tire rubber composition based on at least one diene elastomer, one
reinforcing filler and one chemical crosslinking agent, characterized in
that it comprises the following stages: [0020] grafting, to the diene
elastomer, a modifying agent chosen from the compounds of following
formula (I):

##STR00003##

[0021] where

[0022] R denotes a unit comprising at least one reactive group,

[0023] R1 denotes hydrogen,

[0024] R2 denotes an alkylene radical comprising from 2 to 8 carbon
atoms and optionally one or more heteroatoms chosen from S, N, O or Si,

[0025] A denotes an oxygen or sulphur atom or an ═NH group, preferably
an oxygen atom, [0026] incorporating, in the diene elastomer thus
grafted by the modifying agent, the reinforcing filler, everything being
thermomechanically kneaded, in one or more goes, until a maximum
temperature of between 130° C. and 200° C. is reached,
[0027] cooling the combined mixture to a temperature of less than
100° C., [0028] subsequently incorporating the chemical
crosslinking agent, [0029] kneading everything up to a maximum
temperature of less than 120° C., [0030] extruding or calendaring
the rubber composition thus obtained.

[0031] A further subject-matter of the invention is a process for
preparing a tire rubber composition based on at least one diene
elastomer, one reinforcing filler and one chemical crosslinking agent,
characterized in that it comprises the following stages: [0032]
incorporating, in the diene elastomer, the reinforcing filler and a
modifying agent chosen from the compounds of following formula (I):

##STR00004##

[0033] where

[0034] R denotes a unit comprising at least one reactive group,

[0035] R1 denotes hydrogen,

[0036] R2 denotes an alkylene radical comprising from 2 to 8 carbon
atoms and optionally one or more heteroatoms chosen from S, N, O or Si,

[0037] A denotes an oxygen or sulphur atom or an ═NH group, preferably
an oxygen atom,

[0038] everything being kneaded thermomechanically, in one or more goes,
until a maximum temperature of between 130° C. and 200° C.
is reached, [0039] cooling the combined mixture to a temperature of
less than 100° C., [0040] subsequently incorporating the chemical
crosslinking agent, [0041] kneading everything up to a maximum
temperature of less than 120° C., [0042] extruding or calendaring
the rubber composition thus obtained.

[0043] In particular, the rubber composition included in the tire
according to the invention can be present in at least one semifinished
product made of rubber for the tire, this semifinished product preferably
being chosen from the group consisting of treads, crown reinforcing
plies, sidewalls, carcass reinforcing plies, beads, protectors, rubber
blocks and other internal rubbers, in particular decoupling rubbers,
intended to provide the bonding or the interface between the
abovementioned regions of the tires.

[0045] The invention and its advantages will be easily understood in the
light of the description and implementational examples which follow.

I. MEASUREMENTS AND TESTS USED

[0046] The elastomers and rubber compositions are characterized, before
and after curing, as indicated below.

[0047] Glass Transition Temperature

[0048] The glass transition temperatures Tg of the polymers are measured
using a differential calorimeter ("differential scanning calorimeter").
The analysis is carried out according to the requirements of Standard
ASTM D3418-08.

[0049] Near Infrared Spectroscopy (NIR)

[0050] Near infrared spectroscopy (NIR) is used to quantitatively
determine the content by weight of styrene in the elastomer and its
microstructure (relative distribution of the 1,2-vinyl, 1,4-trans- and
1,4-cis butadiene units). The principle of the method is based on the
Beer-Lambert law generalised for a multicomponent system. As the method
is indirect, it involves a multivariate calibration [Vilmin, F.; Dussap,
C. and Coste, N., Applied Spectroscopy 2006, 60, 619-29] carried out
using standard elastomers having a composition determined by 13C
NMR. The styrene content and the microstructure are then calculated from
the NIR spectrum of an elastomer film having a thickness of approximately
730 μm. The spectrum is acquired in transmission mode between 4000 and
6200 cm-1 with a resolution of 2 cm-1 using a Bruker Tensor 37
Fourier-transform near infrared spectrometer equipped with an InGaAs
detector cooled by the Peltier effect.

[0051] Size Exclusion Chromatography

[0052] Size exclusion chromatography or SEC is used. SEC makes it possible
to separate macromolecules in solution according to their size through
columns filled with a porous gel. The macromolecules are separated
according to their hydrodynamic volume, the bulkiest being eluted first.

[0053] Without being an absolute method, SEC makes it possible to
comprehend the distribution of the molar masses of a polymer. The various
number-average molar masses (Mn) and weight-average molar masses (Mw) can
be determined from commercial standards and the polydispersity index
(Pi=Mw/Mn) can be calculated via a "Moore" calibration.

[0054] Preparation of the Polymer:

[0055] There is no specific treatment of the polymer sample before
analysis. The latter is simply dissolved, in (tetrahydrofuran+1 vol % of
diisopropylamine+1 vol % of triethylamine+1 vol % of distilled water) or
in chloroform, at a concentration of approximately 1 g/l. The solution is
then filtered through a filter with a porosity of 0.45 μm before
injection.

[0056] SEC Analysis:

[0057] The apparatus used is a "Waters Alliance" chromatograph. The
elution solvent is tetrahydrofuran+1 vol % of diisopropylamine+1 vol % of
triethylamine or chloroform, depending on the solvent used for the
dissolution of the polymer. The flow rate is 0.7 ml/min, the temperature
of the system is 35° C. and the analytical time is 90 min. A set
of four Waters columns in series, with commercial names "Styragel HMW7",
"Styragel HMW6E" and two "Styragel HT6E", is used.

[0058] The volume of the solution of the polymer sample injected is 100
μl. The detector is a "Waters 2410" differential refractometer and the
software for making use of the chromatographic data is the "Waters
Empower" system.

[0059] The calculated average molar masses relate to a calibration curve
produced from "PSS ReadyCal Kit" commercial polystyrene standards.

[0060] Tensile Test

[0061] These tensile tests make it possible to determine the elasticity
stresses and the properties at break. Unless otherwise indicated, they
are carried out in accordance with French Standard NF T 46-002 of
September 1988. Processing the tensile recordings also makes it possible
to plot the curve of modulus as a function of the elongation, the modulus
used here being the nominal (or apparent) secant modulus measured in
first elongation, calculated by reducing to the initial cross section of
the test specimen. The nominal secant moduli (or apparent stresses, in
MPa) are measured in first elongation at 10%, 100% and 300% elongation,
respectively denoted MSA10, MSA100 and MSA300.

[0062] The breaking stresses (in MPa) and the elongations at break (in %)
are measured at 23° C.±2° C. and at 100°
C.±2° C., according to Standard NF T 46-002.

[0063] Dynamic Properties

[0064] The dynamic properties ΔE* and tan(δ)max are
measured on a viscosity analyser (Metravib VA4000) according to Standard
ASTM D 5992-96. The response of a sample of vulcanised composition
(cylindrical test specimen with a height of 20 mm and a cross section of
78 mm2), subjected to an alternating sinusoidal stress in
tension/compression, at a frequency of 10 Hz, under standard temperature
conditions (23° C.) according to Standard ASTM D 1349-99 or, as
the case may be, at a different temperature (100° C.), is
recorded. A strain amplitude sweep is carried out from 0.01% to 7%
(outward cycle) and then from 7% to 0.01% (return cycle). The results
made use of are the complex dynamic modulus (E*) and the loss factor
tan(δ). The maximum value of tan(δ) observed, denoted
tan(δ)max, and the difference in complex modulus (ΔE*)
between the values at 0.01% and at 7% strain (Payne effect) are shown for
the return cycle.

II. CONDITIONS FOR IMPLEMENTING THE INVENTION

[0065] As explained above, the rubber composition included in the tire
according to the invention is based on one or more diene elastomers, on
one or more reinforcing fillers, on a chemical crosslinking agent and on
at least one modifying agent of formula (I), and optional additives
conventionally used in tire rubber compositions.

[0066] The expression composition "based on" should be understood as
meaning a composition comprising the mixture and/or the reaction product
of the various constituents used, some of these base constituents being
capable of reacting or intended to react with one another, at least in
part, during the various phases of manufacture of the composition, in
particular during the chemical crosslinking thereof.

[0067] In the present description, unless expressly indicated otherwise,
all the percentages (%) are % by weight. Moreover, any interval of values
denoted by the expression "between a and b" represents the range of
values extending from greater than a to less than b (i.e., limits a and b
excluded), whereas any interval of values denoted by the expression "from
a to b" means the range of values extending from a up to b (i.e.,
including the strict limits a and b).

[0068] II-1. Diene Elastomer

[0069] "Diene" elastomer or rubber should be understood as meaning, in a
known way, an elastomer resulting at least in part (i.e., a homopolymer
or a copolymer) from diene monomers (monomers carrying two carbon-carbon
double bonds which may or may not be conjugated).

[0070] These diene elastomers can be classified into two categories:

[0071] "essentially unsaturated" or "essentially saturated". "Essentially
unsaturated" is understood to mean generally a diene elastomer resulting
at least in part from conjugated diene monomers having a content of units
of diene origin (conjugated dienes) which is greater than 15% (mol %);
thus it is that diene elastomers such as butyl rubbers or copolymers of
dienes and of α-olefins of EPDM type do not come within the
preceding definition and can in particular be described as "essentially
saturated" diene elastomers (low or very low content of units of diene
origin, always less than 15%). In the category of "essentially
unsaturated" diene elastomers, "highly unsaturated" diene elastomer is
understood to mean in particular a diene elastomer having a content of
units of diene origin (conjugated dienes) which is greater than 50%.

[0072] Given these definitions, diene elastomer capable of being used in
the invention is understood more particularly to mean:

[0073] (a) any homopolymer obtained by polymerization of a conjugated
diene monomer having from 4 to 12 carbon atoms;

[0074] (b) any copolymer obtained by copolymerization of one or more
conjugated dienes with one another or with one or more vinylaromatic
compounds having from 8 to 20 carbon atoms;

[0075] (c) a ternary copolymer obtained by copolymerization of ethylene
and of an α-olefin having from 3 to 6 carbon atoms with a
non-conjugated diene monomer having from 6 to 12 carbon atoms, such as,
for example, the elastomers obtained from ethylene and propylene with a
non-conjugated diene monomer of the abovementioned type, such as, in
particular, 1,4-hexadiene, ethylidenenorbornene or dicyclopentadiene;
such polymers are described in particular in the documents WO
2004/035639A1 and US 2005/0239639A1;

[0076] (d) a copolymer of isobutene and of isoprene (butyl rubber) and
also the halogenated versions, in particular chlorinated or brominated
versions, of this type of copolymer.

[0077] Although it applies to any type of diene elastomer, a person
skilled in the art of tires will understand that the present invention is
preferably employed with essentially unsaturated diene elastomers, in
particular of the type (a) or (b) above.

[0078] The following are suitable in particular as conjugated dienes:
1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C1-C5
alkyl)-1,3-butadienes, such as, for example, 2,3-dimethyl-1,3-butadiene,
2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene or
2-methyl-3-isopropyl-1,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene
or 2,4-hexadiene. The following, for example, are suitable as
vinyl-aromatic compounds: styrene, ortho-, meta- or para-methylstyrene,
the "vinyltoluene" commercial mixture, para-(tert-butyl)styrene,
methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene or
vinylnaphthalene.

[0079] The copolymers can comprise between 99% and 20% by weight of diene
units and between 1% and 80% by weight of vinyl-aromatic units. The
elastomers can have any microstructure which depends on the
polymerization conditions used, in particular on the presence or absence
of a modifying and/or randomizing agent and on the amounts of modifying
and/or randomizing agent employed. The elastomers can, for example, be
block, random, sequential or microsequential elastomers and can be
prepared in dispersion, in emulsion or in solution; they can be coupled
and/or star-branched or also functionalized with a coupling and/or
star-branching or functionalization agent. For coupling with carbon
black, mention may be made, for example, of functional groups comprising
a C--Sn bond or of aminated functional groups, such as aminobenzophenone,
for example; for coupling with a reinforcing inorganic filler, such as
silica, mention may be made, for example, of silanol or polysiloxane
functional groups having a silanol end (such as described, for example,
in FR 2 740 778, U.S. Pat. No. 6,013,718 or WO 2008/141702), of
alkoxysilane groups (such as described, for example, in FR 2 765 882 or
U.S. Pat. No. 5,977,238), of aminoalkoxysilane groups (such as described,
for example, in WO 2009/133068), of carboxyl groups (such as described,
for example, in WO 01/92402, U.S. Pat. No. 6,815,473, WO 2004/096865 or
US 2006/0089445) or of polyether groups (such as described, for example,
in EP 1 127 909, U.S. Pat. No. 6,503,973, WO 2009/000750 or WO
2009/000752). Mention may also be made, as other examples of
functionalized elastomers, of the elastomers (such as SBR, BR, NR or IR)
of the epoxidized type, halogenated type, or type comprising carboxylic
acid or anhydride functional groups.

[0080] The following are suitable: polybutadienes, in particular those
having a content (mol %) of 1,2-units of between 4% and 80% or those
having a content (mol %) of cis-1,4-units of greater than 80%,
polyisoprenes, butadiene/styrene copolymers and in particular those
having a Tg (glass transition temperature, measured according to ASTM
D3418) of between 0° C. and -70° C. and more particularly
between -10° C. and -60° C., a styrene content of between
5% and 60% by weight and more particularly between 20% and 50%, a content
(mol %) of 1,2-bonds of the butadiene part of between 4% and 75% and a
content (mol %) of trans-1,4-bonds of between 10% and 80%,
butadiene/isoprene copolymers, in particular those having an isoprene
content of between 5% and 90% by weight and a Tg of -40° C. to
-80° C., or isoprene/styrene copolymers, in particular those
having a styrene content of between 5% and 50% by weight and a Tg of
between 5° C. and -50° C. In the case of
butadiene/styrene/isoprene copolymers, those having a styrene content of
between 5% and 50% by weight and more particularly of between 10% and
40%, an isoprene content of between 15% and 60% by weight and more
particularly between 20% and 50%, a butadiene content of between 5% and
50% by weight and more particularly of between 20% and 40%, a content
(mol %) of 1,2-units of the butadiene part of between 4% and 85%, a
content (mol %) of trans-1,4-units of the butadiene part of between 6%
and 80%, a content (mol %) of 1,2-plus 3,4-units of the isoprene part of
between 5% and 70% and a content (mol %) of trans-1,4-units of the
isoprene part of between 10% and 50%, and more generally any
butadiene/styrene/isoprene copolymer having a Tg of between -5° C.
and -70° C., are suitable in particular.

[0081] To sum up, the diene elastomer or elastomers used in the invention
are preferably chosen from the group of the highly unsaturated diene
elastomers consisting of polybutadienes (abbreviated to "BRs"), synthetic
polyisoprenes (IRs), natural rubber (NR), butadiene copolymers, isoprene
copolymers and the mixtures of these elastomers. Such copolymers are more
preferably chosen from the group consisting of butadiene/styrene
copolymers (SBRs), isoprene/butadiene copolymers (BIRs), isoprene/styrene
copolymers (SIRs) and isoprene/butadiene/styrene copolymers (SBIRs).

[0082] According to a specific embodiment, the diene elastomer is
predominantly (i.e., for more than 50 phr) an SBR, whether an SBR
prepared in emulsion ("ESBR") or an SBR prepared in solution ("SSBR"), or
an SBR/BR, SBR/NR (or SBR/IR), BR/NR (or BR/IR) or also SBR/BR/NR (or
SBR/BR/IR) blend (mixture). In the case of an SBR (ESBR or SSBR)
elastomer, use is made in particular of an SBR having a moderate styrene
content, for example of between 20% and 35% by weight, or a high styrene
content, for example from 35 to 45%, a content of vinyl bonds of the
butadiene part of between 15% and 70%, a content (mol %) of
trans-1,4-bonds of between 15% and 75% and a Tg of between -10° C.
and -55° C.; such an SBR can advantageously be used as a mixture
with a BR preferably having more than 90% (mol %) of cis-1,4-bonds.

[0083] According to another specific embodiment, the diene elastomer is
predominantly (for more than 50 phr) an isoprene elastomer. This is the
case in particular when the compositions of the invention are intended to
constitute, in the tires, rubber matrices of certain treads (for example
for industrial vehicles), of crown reinforcing plies (for example of
working plies, protection plies or hooping plies), of carcass reinforcing
plies, of sidewalls, of beads, of protectors, of underlayers, of rubber
blocks and other internal rubbers providing the interface between the
abovementioned regions of the tires.

[0084] "Isoprene elastomer" is understood to mean, in a known way, an
isoprene homopolymer or copolymer, in other words a diene elastomer
chosen from the group consisting of natural rubber (NR), synthetic
polyisoprenes (IRs), the various copolymers of isoprene and the mixtures
of these elastomers. Mention will in particular be made, among isoprene
copolymers, of isobutene/isoprene copolymers (butyl rubber--IIRs),
isoprene/styrene copolymers (SIRs), isoprene/butadiene copolymers (BIRs)
or isoprene/butadiene/styrene copolymers (SBIRs). This isoprene elastomer
is preferably natural rubber or a synthetic cis-1,4-polyisoprene; use is
preferably made, among these synthetic polyisoprenes, of the
polyisoprenes having a content (mol %) of cis-1,4-bonds of greater than
90%, more preferably still of greater than 98%.

[0085] According to another specific embodiment, in particular when it is
intended for a tire sidewall or for an airtight internal rubber of a
tubeless tire (or other air-impermeable component), the composition
included in the tire in accordance with the invention can comprise at
least one essentially saturated diene elastomer, in particular at least
one EPDM copolymer or one butyl rubber (optionally chlorinated or
brominated), whether these copolymers are used alone or as a mixture with
highly unsaturated diene elastomers as mentioned above, in particular NR
or IRs, BRs or SBRs.

[0086] According to another preferred embodiment of the invention, the
rubber composition comprises a blend of a (one or more) "high Tg" diene
elastomer exhibiting a Tg of between -70° C. and 0° C. and
of a (one or more) "low Tg" diene elastomer exhibiting a Tg of between
-110° C. and -80° C., more preferably between -105°
C. and -90° C. The high Tg elastomer is preferably chosen from the
group consisting of SSBRs, E-SBRs, natural rubber, synthetic
polyisoprenes (exhibiting a content (mol %) of cis-1,4-structures
preferably of greater than 95%), BIRs, SIRs, SBIRs and the mixtures of
these elastomers. The low Tg elastomer preferably comprises butadiene
units according to a content (mol %) at least equal to 70%; it preferably
consists of a polybutadiene (BR) exhibiting a content (mol %) of
cis-1,4-structures of greater than 90%.

[0087] According to another specific embodiment of the invention, the
rubber composition comprises, for example, from 30 to 100 phr, in
particular from 50 to 100 phr, of a high Tg elastomer as a blend with
from 0 to 70 phr, in particular from 0 to 50 phr, of a low Tg elastomer;
according to another example, it comprises, for the whole of the 100 phr,
one or more SBR(s) prepared in solution.

[0088] According to another specific embodiment of the invention, the
diene elastomer of the composition included in the tire according to the
invention comprises a blend of a BR (as low Tg elastomer) exhibiting a
content (mol %) of cis-1,4-structures of greater than 90% with one or
more S-SBR(s) or E-SBR(s) (as high Tg elastomer(s)).

[0089] As explained above, the rubber composition included in the tire
according to the invention is based on at least one diene elastomer and
at least one modifying agent. The diene elastomer can be grafted by the
modifying agent prior to being introduced into the rubber composition, or
else can be grafted by reaction with the modifying agent during the
manufacture of the composition.

[0090] The composition included in the tire according to the invention can
thus comprise just one diene elastomer grafted by the modifying agent
(either grafted prior to being introduced into the composition or grafted
by reaction with the modifying agent during the manufacture of the
composition), or a mixture of several diene elastomers which are all
grafted, or some of which are grafted and the others not, it being
possible for the diene elastomer or elastomers to be used in combination
with any type of synthetic elastomer other than a diene elastomer, indeed
even with polymers other than elastomers, for example thermoplastic
polymers.

[0091] II-2. Modifying Agent

[0092] As explained above, at least one diene elastomer is grafted along
its chain by a modifying agent comprising an associative group, either
prior to being introduced into the composition or by reaction with the
modifying agent during the manufacture of the composition.

[0093] Associative groups is understood to mean groups capable of
associating with one another via nonpermanent physical interactions, such
as ionic interactions, hydrogen bonds, ion-dipole interactions and
dipole-dipole interactions. According to a preferred form of the
invention, they are groups capable of associating via hydrogen bonds and
comprising a nitrogenous heterocycle, preferably a dinitrogenous
heterocycle, generally having 5 or 6 ring members.

[0094] Thus, the grafting along the chain of the elastomer of a modifying
agent carrying an associative group makes it possible to establish,
between the elastomer chains, crosslinking bridges having noncovalent
bonds.

[0095] The modifying agent is chosen from the compounds of following
formula (I):

##STR00005##

[0096] where

[0097] R denotes a unit comprising at least one reactive group,

[0098] R1 denotes hydrogen,

[0099] R2 denotes an alkylene radical comprising from 2 to 8 carbon
atoms and optionally one or more heteroatoms chosen from S, N, O or Si,

[0100] A denotes an oxygen or sulphur atom or an ═NH group, preferably
an oxygen atom.

[0101] Preferably, R denotes an --R3X unit, where R3 denotes a
C2-C50 alkyl radical which can comprise one or more nitrogen,
oxygen, sulphur and silicon atoms and X is a reactive group.

[0102] Reactive group describes the functional group which makes it
possible to establish the grafting with the elastomer. The reactive group
or groups of the R unit can be chosen from amine, thiol, epoxy,
isocyanate, anhydride, alcohol and carboxylic acid groups, preferably
amine and thiol groups.

[0104] According to a preferred embodiment, the content of modifying agent
varies from 0.05 to 10 mol %, preferably from 0.1 to 2 mol % and better
still from 0.2 to 1 mol %.

[0105] II-3. Grafting of the Modifying Agent to the Elastomer

[0106] The grafting of the elastomer takes place by reaction of the said
elastomer with the reactive group or groups carried by the modifying
agent. During this reaction, this reactive group or these reactive groups
form(s) covalent bonds with the chain of the elastomer.

[0107] The grafting of the modifying agent can be carried out neat, for
example in an internal mixer or an external mixer, such as an open mill,
or in solution.

[0108] a) Grafting by the Radical Route

[0109] The grafting of the modifying agent is carried out by radical
grafting, that is to say by a radical reaction between the reactive group
or groups of the modifying agent and one or more double bonds of the
chain of the elastomer.

[0110] The preparation of the diene elastomer grafted along the chain can
be obtained by a radical grafting reaction carried out in solution or
neat using a reactant of mercaptans type, which reaction is intended to
graft the said reactive groups of the modifying agent to the chain of the
starting diene elastomer. The said grafting reaction is optionally
carried out in the presence of a radical initiator, such as a peroxide.

[0111] The grafting process can be carried out continuously or batchwise.
The polymer thus modified can be separated from its solution by any type
of means known to a person skilled in the art, and in particular by a
steam stripping operation.

[0112] b) Grafting to a Premodified Elastomer

[0113] The grafting of the modifying agent can also be carried out via
functional groups present on the ungrafted elastomer. In this case, the
grafting of the modifying agent is carried out by reaction of the
reactive group or groups of the modifying agent with functional groups
present on the ungrafted elastomer. Such functional groups can be chosen
from anhydride, epoxide, halogen and carboxylic acid groups.

[0119] In the case where the reactive group of the modifying agent is an
amine group and where the elastomer has been premodified by epoxy groups,
the grafting reaction is an opening of the epoxide by the amine and this
reaction can be carried out in solution or neat. The said grafting
reaction is optionally carried out in the presence of a base for the
deprotonation of the amine.

[0120] The grafting process can be carried out continuously or batchwise.
The polymer thus modified can be separated from its solution by any type
of means known to a person skilled in the art, in particular by a steam
stripping operation.

[0121] II-2. Reinforcing Filler

[0122] Use may be made of any type of reinforcing filler known for its
abilities to reinforce a rubber composition which can be used in the
manufacture of tires, for example a reinforcing organic filler, such as
carbon black, a reinforcing inorganic filler, such as silica, or also a
blend of these two types of filler, in particular a blend of carbon black
and silica.

[0123] All carbon blacks, in particular blacks of the HAF, ISAF or

[0124] SAF type, conventionally used in tires ("tire-grade" blacks) are
suitable as carbon blacks. Mention will more particularly be made, among
the latter, of the reinforcing carbon blacks of the 100, 200 or 300
series (ASTM grades), such as, for example, the N115, N134, N234, N326,
N330, N339, N347 or N375 blacks.

[0125] Use may also be made, depending on the applications targeted, of
blacks of higher series FF, FEF, GPF, SRF, for example the N660, N683 or
N772 blacks. The carbon blacks might, for example, be already
incorporated in the isoprene elastomer in the form of a masterbatch (see,
for example, Applications WO 97/36724 or WO 99/16600).

[0126] Mention may be made, as examples of organic fillers other than
carbon blacks, of the functionalized polyvinylaromatic organic fillers as
described in Applications WO-A-2006/069792 and WO-A-2006/069793.

[0127] "Reinforcing inorganic filler" should be understood, in the present
patent application, by definition, as meaning any inorganic or mineral
filler, whatever its colour and its origin (natural or synthetic), also
known as "white filler", "clear filler" or even "non-black filler", in
contrast to carbon black, capable of reinforcing by itself alone, without
means other than an intermediate coupling agent, a rubber composition
intended for the manufacture of tires, in other words capable of
replacing, in its reinforcing role, a conventional tire-grade carbon
black; such a filler is generally characterized, in a known way, by the
presence of hydroxyl (--OH) groups at its surface.

[0128] The physical state under which the reinforcing inorganic filler is
provided is not important, whether it is in the form of a powder, of
microbeads, of granules, of beads or any other appropriate densified
form. Of course, reinforcing inorganic filler is also understood to mean
mixtures of different reinforcing inorganic fillers, in particular of
highly dispersible siliceous and/or aluminous fillers as described below.

[0129] Mineral fillers of the siliceous type, in particular silica
(SiO2), or of the aluminous type, in particular alumina
(Al2O3), are suitable in particular as reinforcing inorganic
fillers. The silica used can be any reinforcing silica known to a person
skilled in the art, in particular any precipitated or pyrogenic silica
exhibiting a BET surface and a CTAB specific surface both of less than
450 m2/g, preferably from 30 to 400 m2/g. Mention will be made,
as highly dispersible precipitated silicas ("HDSs"), for example, of the
"Ultrasil 7000" and "Ultrasil 7005" silicas from Degussa, the "Zeosil"
1165 MP, 1135 MP and 1115 MP silicas from Rhodia, the "Hi-Sil EZ150G"
silica from PPG, the "Zeopol" 8715, 8745 and 8755 silicas from Huber or
the silicas with a high specific surface as described in Application WO
03/16837.

[0130] When the composition according to the invention is intended for
tire treads having a low rolling resistance, the reinforcing inorganic
filler used, in particular if it is silica, preferably has a BET surface
of between 45 and 400 m2/g, more preferably of between 60 and 300
m2/g.

[0131] According to the invention, the content of reinforcing filler in
the composition is between 30 and 150 phr, more preferably between 50 and
120 phr. The optimum is different depending on the specific applications
targeted: the level of reinforcement expected with regard to a bicycle
tire, for example, is, of course, less than that required with regard to
a tire capable of running at high speed in a sustained manner, for
example a motorcycle tire, a tire for a passenger vehicle or a tire for a
utility vehicle, such as a heavy duty vehicle.

[0132] According to one embodiment, the reinforcing filler predominantly
comprises silica, the content of carbon black present in the composition
preferably being between 2 and 20 phr.

[0133] According to another embodiment of the invention, the reinforcing
filler predominantly comprises carbon black.

[0134] In order to couple the reinforcing inorganic filler to the diene
elastomer, use is made, in a known way, of an at least bifunctional
coupling agent (or bonding agent) intended to provide a satisfactory
connection, of chemical and/or physical nature, between the inorganic
filler (surface of its particles) and the diene elastomer, in particular
bifunctional organosilanes or polyorganosiloxanes.

[0135] Use is made in particular of silane polysulphides, referred to as
"symmetrical" or "unsymmetrical" depending on their specific structure,
as described, for example, in Applications WO 03/002648 (or US
2005/016651) and WO 03/002649 (or US 2005/016650).

[0136] "Symmetrical" silane polysulphides corresponding to the following
general formula (III):

Z-A-Sx-A-Z, in which: (III) [0137] x is an integer from 2 to 8
(preferably from 2 to 5); [0138] A is a divalent hydrocarbon radical
(preferably, C1-C18 alkylene groups or C6-C12 arylene
groups, more particularly C1-C10, in particular
C1-C4, alkylenes, especially propylene); [0139] Z corresponds
to one of the formulae below:

##STR00006##

[0140] in which: [0141] the R1 radicals, which are unsubstituted or
substituted and identical to or different from one another, represent a
C1-C18 alkyl, C5-C18 cycloalkyl or C6-C18
aryl group (preferably, C1-C6 alkyl, cyclohexyl or phenyl
groups, in particular C1-C4 alkyl groups, more particularly
methyl and/or ethyl), [0142] the R2 radicals, which are
unsubstituted or substituted and identical to or different from one
another, represent a C1-C18 alkoxyl or C5-C18
cycloalkoxyl group (preferably a group chosen from C1-C8
alkoxyls and C5-C8 cycloalkoxyls, more preferably still a group
chosen from C1-C4 alkoxyls, in particular methoxyl and
ethoxyl), are suitable in particular, without the above definition being
limiting.

[0143] In the case of a mixture of alkoxysilane polysulphides
corresponding to the above formula (III), in particular the usual
mixtures available commercially, the mean value of the "x" index is a
fractional number preferably of between 2 and 5, more preferably in the
vicinity of 4. However, the invention can also advantageously be carried
out, for example, with alkoxysilane disulphides (x=2).

[0144] Mention will more particularly be made, as examples of silane
polysulphides, of
bis((C1-C4)alkoxyl(C1-C4)alkylsilyl(C1-C4)a-
lkyl) polysulphides (in particular disulphides, trisulphides or
tetrasulphides), such as, for example, bis(3-trimethoxysilylpropyl) or
bis(3-triethoxysilylpropyl)polysulphides. Use is in particular made,
among these compounds, of bis(3-triethoxysilylpropyl)tetrasulphide,
abbreviated to TESPT, of formula
[(C2HSO)3Si(CH2)3S2]2, or
bis(triethoxysilylpropyl)disulphide, abbreviated to TESPD, of formula
[(C2HSO)3Si(CH2)3S]2. Mention will also be
made, as preferred examples, of
bis(mono(C1-C4)alkoxyldi(C1-C4)alkylsilylpropyl)polys-
ulphides (in particular disulphides, trisulphides or tetrasulphides), more
particularly bis(monoethoxydimethylsilylpropyl)tetrasulphide, as
described in Patent Application WO 02/083782 (or US 2004/132880).

[0145] Mention will in particular be made, as coupling agent other than
alkoxysilane polysulphide, of bifunctional POSs (polyorganosiloxanes) or
of hydroxysilane polysulphides (R2═OH in the above formula III),
such as described in Patent Applications WO 02/30939 (or U.S. Pat. No.
6,774,255) and WO 02/31041 (or US 2004/051210), or of silanes or POSs
carrying azodicarbonyl functional groups, such as described, for example,
in Patent Applications WO 2006/125532, WO 2006/125533, WO 2006/125534 and
WO 2009/062733.

[0146] In the rubber compositions included in the tire according to the
invention, the content of coupling agent is preferably between 0.5 and 12
phr, more preferably between 3 and 8 phr.

[0147] A person skilled in the art will understand that use might be made,
as filler equivalent to reinforcing inorganic filler described in the
present section, of a reinforcing filler of another nature, in particular
organic nature, provided that this reinforcing filler is covered with an
inorganic layer, such as silica, or else comprises, at its surface,
functional sites, in particular hydroxyls sites, requiring the use of a
coupling agent for establishing the bond between the filler and the
elastomer.

[0148] II.3 Chemical Crosslinking Agent

[0149] The chemical crosslinking makes possible the formation of covalent
bonds between the elastomer chains. The chemical crosslinking can be
carried out by means of a vulcanisation system or else by means of
peroxide compounds.

[0150] The vulcanisation system proper is based on sulphur (or on a
sulphur-donating agent) and on a primary vulcanisation accelerator.
Various known vulcanisation activators or secondary accelerators, such as
zinc oxide, stearic acid or equivalent compounds, or guanidine
derivatives (in particular diphenylguanidine), come to be added to this
base vulcanisation system, being incorporated during the first
non-productive phase and/or during the productive phase, as described
subsequently.

[0151] The sulphur is used at a preferred content of between 0.5 and 12
phr, in particular between 1 and 10 phr. The primary vulcanisation
accelerator is used at a preferred content of between 0.5 and 10 phr,
more preferably of between 0.5 and 5.0 phr.

[0152] Use may be made, as (primary or secondary) accelerator of any
compound capable of acting as accelerator of the vulcanisation of diene
elastomers in the presence of sulphur, in particular accelerators of the
thiazole type and their derivatives or accelerators of thiuram, or zinc
dithiocarbamate types. These accelerators are chosen, for example, from
the group consisting of 2-mercaptobenzothiazyl disulphide (abbreviated to
"MBTS"), tetrabenzylthiuram disulphide ("TBZTD"),
N-cyclohexyl-2-benzothiazolesulphenamide ("CBS"),
N,N-dicyclohexyl-2-benzothiazolesulphenamide ("DCBS"),
N-tertbutyl-2-benzothiazolesulphenamide ("TBBS"),
N-tert-butyl-2-benzothiazolesulphenimide ("TBSI"), zinc
dibenzyldithiocarbamate ("ZBEC") and the mixtures of these compounds.

[0153] Preferably, a primary accelerator of the sulphenamide type is used.

[0154] When the chemical crosslinking is carried out using one or more
peroxide compounds, the said peroxide compound or compounds represent
from 0.01 to 10 phr.

[0155] Mention may be made, as peroxide compounds which can be used as
chemical crosslinking system, of acyl peroxides, for example benzoyl
peroxide or p-chlorobenzoyl peroxide, ketone peroxides, for example
methyl ethyl ketone peroxide, peroxyesters, for example
t-butylperoxyacetate, t-butylperoxybenzoate and tbutylperoxyphthalate,
alkyl peroxides, for example dicumyl peroxide, di(t-butyl) peroxybenzoate
and 1,3-bis(tbutylperoxyisopropyl)benzene, or hydroperoxides, for example
t-butyl hydroperoxide.

[0156] II-4. Various Additives

[0157] The rubber composition included in the tire according to the
invention can also comprise all or a portion of the usual additives
generally used in the elastomer compositions intended for the manufacture
of tires, in particular of treads, such as, for example, plasticisers or
extending oils, whether the latter are aromatic or nonaromatic in nature,
pigments, protection agents, such as antiozone waxes (such as Cire Ozone
C32 ST), chemical antiozones, antioxidants (such as 6-PPD), antifatigue
agents, reinforcing resins, methylene acceptors (for example phenolic
novolak resin) or methylene donors (for example HMT or H3M), as
described, for example, in Application WO 02/10269, or adhesion promoters
(for example cobalt salts).

[0158] Preferably, the composition included in the tire according to the
invention comprises, as preferred nonaromatic or very slightly aromatic
plasticizing agent, at least one compound chosen from the group
consisting of naphthenic oils, paraffinic oils, MES oils, TDAE oils,
glycerol esters (in particular trioleates), plasticizing hydrocarbon
resins exhibiting a high Tg preferably of greater than 30° C., and
the mixtures of such compounds.

[0159] The composition included in the tire according to the invention can
also comprise, in addition to the coupling agents, activators of the
coupling of the reinforcing inorganic filler or more generally processing
aids capable, in a known way, by virtue of an improvement in the
dispersion of the inorganic filler in the rubber matrix and of a lowering
of the viscosity of the compositions, of improving their property of
processing in the raw state, these agents being, for example,
hydrolysable silanes, such as alkylalkoxysilanes (in particular
alkyltriethoxysilanes), polyols, polyethers (for example polyethylene
glycols), primary, secondary or tertiary amines (for example
trialkanolamines), hydroxylated or hydrolysable POSs, for example
α,ω-dihydroxypolyorganosiloxanes (in particular
α,ω-dihydroxypolydimethylsiloxanes), or fatty acids, such as,
for example, stearic acid.

[0160] II-5. Manufacture of the Rubber Compositions

[0161] The rubber composition included in the tire according to the
invention is manufactured in appropriate mixers using two successive
preparation phases according to a general procedure well known to a
person skilled in the art: a first phase of thermomechanical working or
kneading (sometimes described as "non-productive" phase) at high
temperature, up to a maximum temperature of between 130° C. and
200° C., preferably between 145° C. and 185° C.,
followed by a second phase of mechanical working (sometimes described as
"productive" phase) at a lower temperature, typically of less than
120° C., for example between 60° C. and 100° C.,
finishing phase during which the chemical crosslinking system is
incorporated.

[0162] According to a preferred embodiment of the invention, all the base
constituents of the composition included in the tire of the invention,
with the exception of the chemical crosslinking system, mainly the
reinforcing filler or fillers or the coupling agent, if appropriate, are
intimately incorporated, by kneading, in the diene elastomer or diene
elastomers during the first "non-productive" phase, that is to say that
at least these various base constituents are introduced into the mixer
and that kneading is carried out thermomechanically, in one or more
stages, until the maximum temperature of between 130° C. and
200° C., preferably of between 145° C. and 185° C.,
is reached.

[0163] According to a first embodiment of the invention, the diene
elastomer has been grafted by the modifying agent prior to the
manufacture of the rubber composition. Thus, in this case, it is the
grafted diene elastomer which is introduced during the first
"nonproductive" phase.

[0164] According to a second embodiment of the invention, the grafting of
the diene elastomer by the modifying agent is carried out concomitantly
with the manufacture of the rubber composition. In this case, both the
diene elastomer, not yet grafted, and the modifying agent are introduced
during the first "non-productive" phase.

[0165] By way of example, the first (non-productive) phase is carried out
in a single thermomechanical stage during which all the necessary
constituents, the optional additional processing aids and various other
additives, with the exception of the chemical crosslinking system, are
introduced into an appropriate mixer, such as a normal internal mixer.
The total duration of kneading, in this non-productive phase, is
preferably between 1 and 15 min. After cooling the mixture thus obtained
during the first non-productive phase, the chemical crosslinking system
is then incorporated at low temperature, generally in an external mixer,
such as an open mill; everything is then mixed (productive phase) for a
few minutes, for example between 2 and 15 min.

[0166] The final composition thus obtained is then calendared, for example
in the form of a sheet or of a plaque, in particular for laboratory
characterization, or else extruded in the form of a rubber profiled
element which can be used, for example, as a tire tread for a passenger
vehicle.

III. EXAMPLES OF THE IMPLEMENTATION OF THE INVENTION

III-1. Radical grafting of
11-mercapto-N-(2-(2-oxoimidazolidin-1-yl)ethyl)undecanamide to an SBR
elastomer

[0167] 1) Starting Elastomer Used:

[0168] Use is made, as starting elastomer, of the copolymer of styrene and
butadiene (SBR) prepared in solution exhibiting the following
microstructure characteristics, determined by 1H NMR:

[0169] content by weight of styrene units: 26.5%

[0170] content by weight of 1,2-(vinyl) structures in the units resulting
from a butadiene: 24.0%.

[0172] In the tests which follow, the ungrafted SBR elastomer (control
elastomer) is denoted as SBR-A and the grafted elastomer is denoted
SBR-B.

[0173] 2) Implementation of the Radical Grafting:

[0174] 300 g of antioxidized SBR are dissolved in 2.7 l of cyclohexane in
a 10 l jacketed reactor.

[0175] At the same time, a solution of lauroyl peroxide (0.717 g, 1.8
mmol) in cyclohexane (100 ml) and a solution of
11-mercapto-N-(2-(2-oxoimidazolidin-1-yl)ethyl)undecanamide (14.2 g,
43.16 mmol) in dichloromethane (720 ml) are prepared. The amount of
peroxide introduced is such that the mercaptan/peroxide molar ratio is
equal to 24. The peroxide solution and the mercaptan solution are
introduced successively into the elastomer solution.

[0176] The modifying agent,
11-mercapto-N-(2-(2-oxoimidazolidin-1-yl)ethyl)undecanamide, has the
following formula:

##STR00007##

[0177] The mixture is subsequently stirred at 80° C. for 4 h and
then 31 ml of a 50 g/l solution of 6-PPD
(N-(1,3-dimethylbutyl)-N'-phenylp-phenylenediamine) in methylcyclohexane
are added. The reaction mixture is stirred at 80° C. for 15
minutes. The polymer is separated from its solvent by a stripping
operation (steam distillation) in the presence of Tamol® and calcium
chloride. The stripped polymer is squeezed free from solvent on rollers
and finally dried in an oven at 60° C. under reduced pressure and
under a stream of nitrogen.

[0179] The grafted elastomer (SBR-B) thus produced exhibits a content of
11-mercapto-N-(2-(2-oxoimidazolidin-1-yl)ethyl)undecanamide of 0.16 mol
%.

Measurement of the content of
11-mercapto-N-(2-(2-oxoimidazolidin-1-yl)ethyl)undecanamide

[0180] The content of grafted
11-mercapto-N-(2-(2-oxoimidazolidin-1-yl)ethyl)undecanamide is determined
by an NMR analysis. The spectra are acquired on a Bruker 500 MHz
spectrometer equipped with a 5 mm BBIz-grade "broad band" probe. The
quantitative 1H NMR experiment uses a simple 30° pulse
sequence and a repetition time of 3 second between each acquisition. The
samples are dissolved in carbon disulphide (CS2). 100 μl of
deuterated cyclohexane (C6D12) are added for the lock signal.

[0181] The 1H NMR spectrum makes it possible to quantify the grafted
11-mercapto-N-(2-(2-oxoimidazolidin-1-yl)ethyl)undecanamide units by
integration of the signals characteristic of the CH2N protons, which
appear at a chemical shift of between δ=3-3.5 ppm

III-2. Preparation of the Compositions

[0182] The following procedure is used for the tests which follow: the
diene elastomer or elastomers (grafted or ungrafted), the optional
reinforcing filler or fillers and the optional coupling agents are
introduced into an internal mixer, which is 70% filled and which has an
initial vessel temperature of approximately 90° C., followed,
after kneading for one to two minutes, with the various other
ingredients, with the exception of the vulcanisation system.
Thermomechanical working (non-productive phase) is then carried out in
one stage (total kneading time equal to approximately 5 min), until a
maximum "dropping" temperature of between 110° C. and 190°
C., preferably between 130° C. and 180° C., is reached. The
mixture thus obtained is recovered and is cooled, and then the
vulcanisation system (sulphur) is added on an external mixer
(homofinisher) at a temperature of less than 120° C., for example
between 60 and 100° C., everything being mixed (productive phase)
for approximately from 5 to 6 min.

[0183] The compositions thus obtained are subsequently calendared, either
in the form of plaques (thickness of 2 to 3 mm) or of thin sheets of
rubber, for the measurement of their physical or mechanical properties,
or in the form of profiled elements which can be used directly, after
cutting to and/or assembling at the desired dimensions, for example as
semifinished products for tires, in particular as treads for tires.

III-3 Characterization Tests--Results

[0184] The object of this example is to compare the properties of a rubber
composition according to the invention, comprising a grafted SBR-B
elastomer (composition 3), with two comparative compositions comprising
an ungrafted SBR-A elastomer (compositions 1 and 2).

[0185] The rubber compositions are given in Table 1. The amounts are
expressed in parts per 100 parts by weight of elastomer (phr).

[0186] As shown in the above table, the control compositions 1 and 2
differ from one another in different sulphur contents (the CBS content,
which is also different, being adjusted with regard to the sulphur
content).

[0187] Composition 3 in accordance with the invention exhibits a sulphur
content (and also the CBS content adjusted to this sulphur content) which
is lower than that of compositions 1 and 2.

[0188] Results

[0189] The properties after curing, measured at 23° C. and
100° C., are given in Table 2.

[0190] Between compositions 1 and 2, there is observed, as expected, an
increase in the MSA moduli for the composition 2, which comprises a
higher sulphur content, bringing about greater crosslinking at 23°
C. and at 100° C. There is also observed, at 23° C. and at
100° C., a poorer elongation at break (lower value of the
elongation at break) for the composition 2 than for the composition 1;
results also expected by a person skilled in the art in the light of the
contents of crosslinking agents of these 2 compositions.

[0191] The hysteresis properties (reflected by the measurement at
100° C. of tan(δ)max) are improved in the composition 2
with respect to the composition 1. This is known to a person skilled in
the art and is explained by an increase in the sulphur content in the
composition 2, bringing about a greater crosslinking density.

[0192] Furthermore, it is observed, surprisingly, that the composition 3
in accordance with the invention, including a grafted polymer and also a
lower content of crosslinking agent than the compositions 1 and 2,
exhibits MSA moduli at 23° C. which are between those of the
compositions 1 and 2 but with a very marked improvement in the elongation
and breaking stress properties with respect to the two control
compositions 1 and 2, whereas, when the MSA moduli increase (composition
3 with respect to the composition 1), a person skilled in the art expects
to see a deterioration in the elongation and the breaking stress, as may
be observed for the composition 2 with respect to the composition 1.

[0193] The same phenomenon is observed at 100° C., which is further
accompanied, very surprisingly, by a very strong fall in the hysteresis
(much smaller tan δmax value) and by a significant decrease in
the Payne effect (much lower ΔE*) with respect to the two control
compositions 1 and 2.

[0194] It is thus found that the rubber compositions in accordance with
the invention, which undergo both chemical crosslinking and physical
crosslinking, make it possible, despite a lower content of crosslinking
agent, to obtain high MSA moduli while significantly enhancing the
elongation at break and breaking stress properties and while also very
greatly lowering the hysteresis of the composition.